Tuning fork type oscillators



April 2, 1963 H. REIFEL 3,083,607

TUNING FORK TYPE OSCILLATORS F Filed Jan. 10, 1961 United States Patent 3,83 ,607 TUNING FGKK TYPE OSULLATORS Harry Reifel, Waltharn, Mass, assignor to Stevens- Arnold lino, South Boston, Mass. Filed Jan 10, N61, $62. No. 81,873 1 Claim. (Cl. S4409) This invention relates to tuning fork type oscillators, has as objects to simplify, and to reduce the costs of such oscillators.

Tuning fork type oscillators usually have a pair of reeds of magnetic spring metal, connected together at corresponding ends. One reed is usually vibrated by an electromagnet acting as a motor, which is supplied with A.C. by an oscillator, and vibrates :the other reed in tuning dork action. Another electromagnet acting as a generator has voltages induced in it by vibration of the other reed, which are regeneratively fed back to the oscillator circuit, and are supplied to the load as take-oft" voltages. The reeds should be resonant at the applied A.C. frequency.

This invention simplifies the construction of, and the mounting of such reeds by forming a pair of such reeds and their interconnection in one piece, the interconnection being formed as a fiat strip with the reeds at its center, and having ends extending substantially beyond the reeds. The reeds are attached to their associated oscillator frame by screws extending through the ends of the strap. The reeds need not be so precisely formed as formerly required since their nodal point will shift along their interconnecting strap when the two reeds do not have exactly the same lengths, until their lengths are effectively the same.

This invention will now be described with reference to the annexed drawings, of which:

FIG. 1 is a top plan view of an oscillator embodying this invention;

FIG. 2 is a section along the lines 22 of FIG. 1;

SIG. 3 is a projected View of the pair of reeds used, an

FIG. 4 is a circuit schematic showing the electromiagnets of the oscillator connected in a transistor-driven oscillator circuit.

A base it) of electric insulation has attached to its top, along opposite sides thereof, a pair of generally U-shaped brackets 11 and 12 to which are attached by screws 13 and 14 respectively, a pair of side plates 15 and 16 respectively, of magnetic metal. The brackets 1 1 and 12 have their legs formed as lugs 17 and 13 respectively, which contain tapped openings 19 and 2% respectively, for receiving screws which are not shown, for attaching a housing which is not shown.

Spacers 21 with the lower end of a magnetic shield 22 therebetween, are clamped between the brackets 11 and 12;. A pair of spacers 23 and 24 extend between opposite ends of the tops of the plates 15 and lo, and are attached to the plates 15 and 16 by the screws 25 and 2-6 respectively.

interconnecting strap 27 of reeds 28 and 29 extends across the spacers 23 and 24 at their centers, and is attached at its ends to the spacers 23 and 24 by screws 3d and 31 respectively. The strap 27 and the reeds 28 and 2 9 are formed in one piece from magnetic spring metal. The ends of the strap 27 which are attached to the spacers 23 and 24, extend substantial distances from the reeds 28 and 29 so that the portion of the strap 27 which extends between the reeds is floating.

The magnetic shield 22 extends midway between the reeds 2S and 29, and is attached at its upper end by spacers 33 and screws 34 and 35 to the side plate 15.

A pair of permanent magnets 38 and 39 are attached to the inner sides of the upper portion of the side plates 15 and 165 respectively, opposite the upper ends of the EfihSfiW Patented Apr. 2, 1953 'ice reeds 28 and 29 respectively, and serve to nragnetize the reeds.

An electromagnet 4t) is attached to the inner side of the plate 15 by a bolt 41, opposite the outer side of the lower portion of the reed 28, and has a pole-piece i-2 adjacent to the reed 28. A similar eleotroniagnet 44 is attached to the inner side of the side plate 16 by a bolt 45, opposite the outer side of the lower portion of the reed 29, and has a pole-piece 46 adjacent to the reed 2-9.

There is a magnetic circuit through the magnet '38, the reed 28, the pole-piece 42, the side plate 15 and b ack to the magnet 38. There is a similar magnetic circuit from the magnet 39, through the reed 29, the pole-piece 4 6, and the side plate '16 back to the magnet 39. The shield 22 prevents the field of the electroniagnet it) from directly affecting the reed 29, and prevents the field of the electromagnet 44 from directly affecting the reed 28.

The base lil has a socket guide 5%, and socket prongs 51 for connecting the components of the oscillator to external circuits.

As shown by FIG. 4, one end of the electromagnet 49 would be connected to the collector electrode of a transistor 54, with its other end connected to the negative terminal of a battery which is not shown. One end of the electromagnet 44 would be connected to the base electrode of the transistor, with its other end connected to the junction of resistors 55 and 56 which are connected in series across the battery. The emitter of the transistor is connected in series with variable resistor 57 to the positive terminal of the battery. The signal currents would be taken from across the electromagnet 44 by the output connections 53 and 59.

The electromagnet is a motor which vibrates the reed 2? and the electromagnet 44 is a generator in which currents are induced by vibration of the reed 29. When the circuit shown by FIG. 4 is completed by connection to a battery, it is shock excited into oscillation, the AC. oscillatory currents being fed through the electromagnet it? for vibrating the reed 28. The attraction between the reed 2S and the pole-piece 42 of the electrcmagnet 4% would either be increased or decreased depending upon the instantaneous polarity of the applied AC. voltage, causing the reed 28 to vibrate at the applied frequency to which it should be resonant. The reed 29 would be vibrated by the vibrations of the reed 23 applied to it through the interconnecting strap 27. The currents induced in the electromagnet 44 by the vibration of the reed 29, would be regenenatively fed back to the input of the transistor for maintaining the circuit of the latter in oscillation, and would be taken off through the connections 58 and 59 for supply to the load. A vacuum tube could be used instead of the transistor.

The strap 27 through being supported at its ends and not where it connects the reeds, permits, when the two reeds do not have precisely the same resonant frequency as by one reed being slightly longer than the other, the nodal point to be displaced from the center of the portion of the strap which connects the reeds, to one side of the center sulficiently to cause the effective lengths of the reeds to be the same.

What is claimed is:

A tuning fork type oscillator comprising a base of electric insulation, a pair of aligned, parallel, spaced-apart plates of magnetic metal attached at corresponding ends to said base, a pair of spaced-apart, aligned, parallel spacers extending between and attached [to the other ends of said plates, a strap of spring metal extending over and connected at its ends to said spacers, a pair of aligned, spaced-apart, parallel reeds of magnetic spring metal having corresponding ends connected to the central portion of said strap between said ends of said strap, an electromagnet [for vibrating one of said reeds attached to the inner side of one of said plates adjacent to the free end of said one reed, a second electromagnet in which currents are induced :by the vibrations of the other of said reeds attached to the inner side of theo-therof said-plates adjacent to the free end of said other reed, a shield sheet of miagnetiemetal'attnched to one of said plates and extending midway between said reeds parallel thereto, a permanent magnet for magnetizing said one reed attached to said one plate and having an end'adj'acent tothe other end of said one reed, and another permanent magnet :for

magnetizing said other-reed attached to said other pla-te and having an end adjacent to the other end of said other reed.

References Cited in the file of this patent UNITED STATES PATENTS 

